1. Field of the Invention
The present invention relates to a tool presetter to be mounted in a machine tool having a pivotal tool spindle stock, and to a tool offset amount calculation method for use in a machine tool of this type.
2. Description of Related Art
In recent years, some of composite lathes adapted for cutting, milling and drilling have been further adapted for oblique drilling. Such a composite lathe has a tool spindle stock to which various types of tools retained in a tool magazine are selectively attached in a detachable manner by means of an automatic tool changer (ATC).
The composite lathe of this type includes, for example, a headstock 12 fixedly provided at one end of a bed 11, and a tailstock 13 provided movably along the Z-axis at the other end of the bed 11 as shown in FIG. 3. A saddle 14 is provided movably along the Z-axis on the bed 11 between the headstock 12 and the tailstock 13. A column 15 movable forwardly and backwardly of the bed 11 is provided upright on the saddle 14, and a support base 16 for supporting a tool spindle stock 17 is provided movably along the X-axis on a slanted surface of the column 15. The tool spindle stock 17 is supported pivotally about a B-axis by the support base 16. Therefore, a tool spindle can be set at any given angle with respect to a main spindle by pivoting the tool spindle stock 17 about the B-axis in the composite lathe, so that an oblique drilling operation can be performed on a workpiece fixed to the main spindle.
The composite lathe is provided with a built-in tool presetter. When tool offset amounts are to be measured, a presetter arm (not shown) having a presetter sensor provided at a distal end thereof for contact with a tool nose is moved into a machining region toward the tool spindle stock 17 from the headstock 12.
Where the tool offset amounts are determined by means of the built-in tool presetter mounted in the composite lathe having the pivotal tool spindle stock 17, the tool spindle stock 17 is pivoted by xe2x88x9290 degrees so as to position the tool spindle parallel to the Z-axis as shown in FIG. 4 and, in this state, a nose of a tool T attached to the tool spindle stock 17 is brought into contact with a Z-axis detection point and an X-axis detection point of the presetter sensor 18 located at a predetermined position within the machining region, whereby Z-axis and X-axis machine coordinate values Zm, Xm of the tool spindle stock 17 are determined with the tool nose being in contact with the detection points of the presetter sensor 18. Then, reference tool offset amounts Lz, Lx are calculated on the basis of the machine coordinate values Zm, Xm and machine coordinate values A, B of the Z-axis and X-axis detection points of the presetter sensor 18. More specifically, the Z-axis reference tool offset amount Lz and the X-axis reference offset amount Lx are defined by Axe2x88x92Zm and Bxe2x88x92Xm, respectively, in the built-in tool presetter. It is noted that the X-axis tool offset amount is on a diametrical basis in the lathe system, so that the X-axis reference offset amount is Lx xc3x972 in practical applications.
As described above, the tool spindle stock 17 is pivoted so as to position the tool spindle parallel to the Z-axis, and the tool nose is brought into contact with the presetter sensor 18 for the determination of the reference tool offset amounts Lz, Lx by means of the built-in tool presetter. Where a cutting tool as shown in FIGS. 5A and 5B is attached to the tool spindle stock 17 at an angle with respect to the tool spindle, for example, it is impossible to bring a nose of the tool into contact with the Z-axis and X-axis detection points of the presetter sensor 18, depending on the shape of the tool T and the shape of a tool holder H which holds the tool.
Even in the case of the tool T having such a shape, the tool nose may be brought into contact with the Z-axis and X-axis detection points of the presetter sensor 18 (see FIGS. 7A and 7B) by pivoting the tool spindle stock 17 as shown in FIG. 6. However, the conventional tool presetter is adapted to calculate the reference tool offset amounts Lz, Lx on the basis of the machine coordinate values A, B of the Z-axis and X-axis detection points of the presetter sensor 18 and the machine coordinate values Zm, Xm determined with the tool nose brought into contact with the detection points of the presetter sensor 18 by pivoting the tool spindle stock 17 by xe2x88x9290 degrees as described above. Therefore, it is impossible to accurately determine the reference tool offset amounts Lz, Lx even if the tool nose is brought into contact with the presetter sensor 18 by pivoting the tool spindle stock 17.
Where the reference tool offset amounts Lz, Lx are determined for the tool T of the aforesaid type, the tool nose cannot be brought into contact with the X-axis detection point of the presetter sensor 18 with the tool spindle being positioned parallel to the Z-axis for the determination of the X-axis tool offset amount Lx. Therefore, the tool nose is moved to the same level as the X-axis detection point while the tool nose is visually observed in the vicinity of the presetter sensor 18, and then the X-axis detection point is touched by a finger F or the like as shown in FIG. 8. Thus, the determination of the X-axis reference offset amount is achieved analogously to the case where the tool nose can be brought into contact with the X-axis detection point.
However, the X-axis reference tool offset amount Lx thus determined is not sufficiently accurate. Therefore, a sample workpiece is actually machined after the reference tool offset amount Lx thus determined is inputted in an NC machine, and then it is checked if the sample workpiece is properly machined. If the sample workpiece is not properly machined, the determined reference tool offset amount Lx is modified. This checking and modifying operation is troublesome.
In view of the foregoing, it is an object of the present invention to provide a tool presetter and a tool offset amount calculation method which ensure easy and accurate determination of reference tool offset amounts for a machine tool, such as the aforesaid composite lathe, which has a pivotal tool spindle stock.
In accordance with a first aspect of the present invention to achieve the aforesaid object, there is provided a tool presetter to be mounted in a machine tool having a pivotal tool spindle stock, the tool presetter comprising: a presetter sensor provided at a predetermined position; and control means which determines machine coordinate values of the tool spindle stock when a nose of a tool attached to the tool spindle stock is in contact with the presetter sensor and, on the basis of the machine coordinate values and a pivot angle of the tool spindle stock detected when the tool nose is in contact with the presetter sensor, calculates a reference tool offset amount as measured along a control axis with the tool spindle stock being set to position a tool spindle parallel to the control axis.
With this arrangement, the tool presetter calculates the reference tool offset amount as measured along the control axis with the tool spindle stock being set to position the tool spindle parallel to the control axis on the basis of the machine coordinate values determined when the tool nose is in contact with the presetter sensor and the pivot angle of the tool spindle stock detected when the tool nose is in contact with the presetter sensor. Therefore, there is no need to set the tool spindle stock to position the tool spindle parallel to the control axis when the tool nose is brought into contact with the presetter sensor, so that the tool nose contacting operation can more flexibly be performed.
Particularly in the case of a tool having a shape such that a tool nose thereof cannot be brought into contact with the presetter sensor with the tool spindle stock being set to position the tool spindle parallel to the control axis, a tool offset amount calculation method according to a second aspect of the present invention may be employed wherein, after the tool spindle stock is pivoted from a position at which the tool spindle is parallel to the control axis to bring the tool nose into contact with the presetter sensor, the machine coordinate values of the tool spindle stock are determined when the tool nose is in contact with the presetter sensor, and then the reference tool offset amount as measured along the control axis with the tool spindle stock being set to position the tool spindle parallel to the control axis is calculated on the basis of the machine coordinate values and the pivot angle of the tool spindle stock. With this arrangement, there is no need to perform the troublesome operation for checking and modifying the determined reference tool offset amount, unlike the tool offset amount calculation method employing the conventional tool presetter which cannot properly determine the reference tool offset amount unless the tool spindle stock is set to position the tool spindle parallel to the control axis. Thus, the inventive tool offset amount calculation method can assuredly and accurately determine the reference tool offset amount in a short time.